SOD is a member of a family of superoxide dismutases which, because of their ability to catalyze the destruction of superoxide ions, renders them useful in a variety of therapeutic settings such as in reducing perfusion injury and in treating inflammation. The amino acid sequence of human SOD (hSOD) is described in Jabusch et al, Biochemistry (1980) 19:2310-2316. The cloning and sequencing of hSOD cDNA and the production of hSOD in bacteria and yeast are described in EPA 84111416.8 (published Apr. 24, 1985 under number 0 138 111). hSOD is normally a homodimer of two chains bound together by hydrophobic interaction. The homodimer has a molecular weight of approximately 32 kd.
SOD is rapidly removed from circulation by the kidney. Rat studies indicate its half-life in serum is on the order of seven minutes. The limited circulatory life of injected SOD may severely limit clinical approaches to SOD pharmacology and the effectiveness of treatment. In order to eliminate SOD's susceptibility to removal by the kidney, prior workers have conjugated SOD with macromolecules such as Ficoll (PNAS, USA (1980) 77:1159-1163), polyethylene glycol (Res. Commun. in Chem. Path. & Pharmacol. (1980) 29:113-120; Pharmacol. Res. Commun. (1982) 14:113-119; Anal. Biochem. (1983) 131:25-30; and J. Pharm. & Pharmacol. (1983) 35:757-763), and human serum albumin (Agents Actions (1980) 10:231-240). SOD has been entrapped in liposomes for the same purpose (J. Clin. Invest. (1984) 73:87-95; Fed. Proc. (1985) 44:2591-2595).
An object of the present invention is to provide SOD in a novel polymeric form that has an extended circulatory life and retains the activity of SOD. This polymeric SOD may be made using recombinant DNA techniques. Its manufacture does not involve any chemical derivatization such as that described above. A preferred embodiment of this polymeric SOD comprises SOD monomers covalently linked to each other via a polypeptide that has an amino acid sequence, such as the sequence of the hinge region of immunoglobulin, which naturally acts as a means of coupling functional domains of biologically active proteins in a manner that allows them to fold and function independently. In this regard, Staphylococcus aureus nuclease and the c-myc oncogene have both been attached to a murine immunoglobulin heavy chain via the hinge region of the immunoglobulin to produce functional antibody-enzyme complexes (Nature (1984) 312:604-608).